Vaccination in Shelter Animal Populations

Vaccinations are a critical piece of shelter operations to minimize disease transmission and keep shelter populations healthy. Many vaccinations can protect against disease within hours. Some vaccines actually prevent disease, while others reduce the severity of disease. Because we often do not know the vaccination history of animals entering shelters and the risk of exposure is often greater than in a typical home setting, vaccination remains an essential part of the intake process.

Within a shelter population, there will always be risk of disease due to animals arriving without proper immunity. One of the best ways to protect against infectious diseases is to follow vaccination schedules for shelter animals that generally begin at a younger age and include more frequent re-vaccination. These recommendations also include vaccinating virtually all animals at or prior to intake to help ensure protection for individual animals as well as a higher level of herd immunity in the shelter population. This process can help to contain any disease to one or few animals and reduce the overall risk of a disease because a high percentage of the population will be protected through vaccination.

Vaccination Storage/Handling

Most vaccines recommended for use in shelters contain living organisms. It is very important to have proper storage, handling, and administration to ensure the organisms remain viable and able to induce a protective immune response.

Learn more about vaccine administration, handling, and storage.

Shelter Vaccination Strategies

Vaccination is a medical procedure, so oversight of vaccine protocols must be directed by a veterinarian. Vaccine administration for every animal at or before intake is a critical practice in minimizing infectious disease and preventing widespread outbreaks. Modified live vaccinations (MLV) are strongly recommended over killed or inactivated vaccinations. Most animals will respond to a single MLV vaccine very quickly: in as little as 24 hours for canine distemper or 72 hours for canine parvovirus or panleukopenia. When killed products are used, there is a significant delay in the onset of protective immunity. In addition, MLV vaccines are better able to override maternal antibody interference in puppies and kittens.

Kittens and puppies need frequent core vaccines due to maternal antibodies, which can inhibit vaccine effectiveness in a process called maternal antibody interference. These are protective immune molecules that are transferred from mothers and protect young animals while their immune system is maturing. Some antibodies cross the placenta, but the majority are obtained during early nursing. The amount of maternal antibodies passed onto a kitten or puppy can be quite variable due to things like the mother’s vaccine history and prior natural exposure to disease. These antibodies only provide temporary protection, however, as their levels decline over time. 

In shelter medicine, a practical strategy used to overcome the interference of maternal antibodies is to begin vaccinating as early as possible, which is approximately 4 weeks of age. Because we don’t know when the maternal antibodies will decrease enough to allow the vaccine to be effective, we continue to vaccinate at frequent intervals until we can be sure there are no maternal antibodies remaining. This is typically every 2-3 weeks until 20 weeks of age to minimize the “window of susceptibility”, the time when maternal antibody levels aren’t sufficient to protect against disease but can still block the young animal’s own immune response. The key concept is not that a certain number of vaccines are administered per kitten or puppy, but the vaccines are given at appropriate intervals until the animal has reached an age when maternal antibody interference is no longer a concern, typically at 5 months of age.

Core vaccinations for dogs include:

• Modified-live or recombinant Canine Distemper Virus, Adenovirus-2, Parvovirus, Parainfluenza (DA2PP)
• Intranasal Bordetella bronchiseptica and Canine Parainfluenza Virus, with or without Canine Adenovirus-2

Core vaccinations for cats include:

• Modified-live Feline Viral Rhinotracheitis, Calicivirus, Panleukopenia (FVRCP)

Learn vaccine recommendations for shelter dogs and shelter cats.

Vaccinating Special Populations

Vaccinating can be a lifesaving procedure, but it is a medical intervention that is not without risks. Many animals in shelters have not had natural or vaccine exposure to common diseases, so the benefit of immediately vaccinating every animal over 4 weeks of age on intake typically outweighs the risks. In general, the recommendation is that every animal housed in a shelter is vaccinated with core vaccinations except in extraordinary circumstances.

Below are guidelines to help shelter personnel make decisions about vaccinating individual animals with specific conditions. When making difficult vaccination decisions, it's best to consult the veterinarian your shelter works with and consider the overall benefit and risk to each individual animal as well as the shelter population as a whole.

• Sick Animals: Animals in shelters with mild illness (such as minor upper respiratory disease) should receive core vaccines. For animals with more serious conditions, your veterinarian can help determine your shelter’s protocol. Consult your veterinarian in all cases of unusual illness or where an animal has a high body temperature.
• Lactating Animals: There are minimal risks to the nursing babies when moms are vaccinated, so vaccination of all lactating cats or dogs is recommended on intake.
• Pregnant Animals: There are some risks to unborn kittens when using modified live vaccines, especially at certain stages of gestation. The risk to unborn puppies is much less well understood. The ASPCA recommends that shelters consider the risk of infectious disease to pregnant animals when weighing vaccination decisions. In many cases where disease risk is significant (e.g., pregnant animals entering a shelter environment), vaccination is advised. If animals will soon be spayed, vaccination is also advised.
• Injured Animals: In most cases, vaccinating injured animals is the recommended course of action, especially if the injury is not severe.
• Foster Animals: Foster homes are considered to be extensions of the shelter environment and so animals in foster care generally fall under the same vaccination recommendations as shelters.  For instance, puppies and kittens receive vaccinations beginning at 4 weeks of age and continuing every 2 weeks up to 20 weeks or for as long as the animals remain in the foster home or shelter’s care. The interval can sometimes be increased to every 3-4 weeks for kittens and puppies in a low-risk foster home setting. Low-risk foster homes include those where sanitation and infection control protocols are properly followed, only one animal or litter is fostered at a time, and there is no significant concern about exposure to infectious disease from any previous foster or neighborhood animals.

See this Vaccination Decision Table for a quick view.

Related Webinars

• Shelter Intake Part 1
• Shelter Intake Part 2

Additional Vaccination Resources

ASV Guidelines for Standards of Care in Animal Shelters (Medical Health, p. 29)